The relation of teleological to causal explanations in psychology is examined. Nagel's claim that they are logically equivalent is rejected. Two arguments for their non-equivalence are considered: (i) the impossibility of specifying initial conditions in the case of teleological explanations and (ii) the claim that different kinds of logic are involved. The view that causal explanations provide only necessary conditions whereas teleological explanations provide sufficient conditions is rejected: causal explanations can provide sufficient conditions, typically being unable to provide necessary ones, whereas teleological explanations tend to point to necessary features. Nor is a distinction in terms of intensional and extensional logic entirely satisfactory, although there is some support for the view that teleological and causal explanations invoke different types of explanatory framework. A key feature of teleogical explanation is the achievement of the same goal by a variety of means. Thus its main scientific function is likely to be heuristic rather than predictive.